The conventional tone control circuit for the hearing aid including a control circuit at high frequency and low frequency is provided so as to control independently through the capacitor-resistor circuit and resistor-capacitor circuit as shown in FIG. 7.
Therefore, since the control points are divided by two points, it is too hard to control by the user of the hearing aid. In addition, since the loudness (sensuous volume) changes when the voice is output even though it is controlled, the user has to control the tone and volume at the same time, and it is hard to control by the user. So the user requests the doctor, specialists, to make adjustments. Therefore, it is hard to keep the comfortable state to use the user always.